Contagium v1.2b

Phase One: Infection has begun and it is spreading silently
Phase Two: Liberty City is on red alert. Infected population is rising and authorities are trying to keep down the infection. If you give them some help killing infected they won't bother you
Phase Three: Liberty City has been evacuated. From now on everything you have to do is survive

Infected are contagious but some people are immune to the virus.

Both Phase One and Phase Two depends on the infected population. Phase Three begins if you are hit and faint.